Legionnaire Disease and Pontiac Fever (cont.)

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How common is Legionnaires' disease?

It is estimated that approximately 10,000 to 15,000 people contract Legionnaires' disease in the United States each year. Legionnaires' pneumonia is not uncommon. In fact, it represents over 4% of all community-acquired pneumonias. An additional unknown number of people are infected with the Legionella bacterium but have only mild symptoms or no symptoms at all (so-called Pontiac fever).

Outbreaks of Legionnaires' disease have received the most media attention. A recent outbreak was associated with a party at the Playboy mansion in Los Angeles where at least four individuals contracted Legionnaires' disease. However, the disease most often occurs as single, isolated cases not associated with any identified outbreak. Outbreaks are usually recognized in the summer and early fall, but cases may occur year-round. About 5%-15% of known cases of Legionnaires' disease have been fatal.

Since the bacterium of Legionnaires' disease was identified in 1976, numerous hospital-acquired outbreaks of the disease have also been reported. These outbreaks have enabled researchers to study epidemics of legionellosis.

What are the usual symptoms of Legionnaires' disease?

Patients with Legionnaires' disease usually develop a fever, chills, and a cough. The cough may either be dry or produce sputum. Some patients with Legionnaires' disease also have muscle aches, headache, tiredness, loss of appetite, and occasionally diarrhea. Legionnaires' disease can cause a severe pneumonia, seriously affect breathing, even lead to respiratory failure and adult respiratory distress syndrome (ARDS). In some cases, the heart rate is slower than expected for the degree of fever. There are no specific symptoms that directly identify Legionnaires' pneumonia. Legionnaires' pneumonia presents in a manner similar to Chlamydia pneumonia and Mycoplasma pneumonia, so-called atypical pneumonias (previously referred to as "walking pneumonia"). These are referred to as atypical because, unlike typical pneumonia (as characterized by Streptococcus pneumonia), which involves high, spiking fevers, sudden onset, cough, and purulent sputum and often chest pain and a localized infiltrate on chest X-ray. They can have a less virulent presentation despite very diffuse infiltrates on chest X-ray.

People with Pontiac fever experience a self-limiting influenza-like illness with fever, chills, headache, and muscle aches but, by definition, do not have pneumonia. Affected individuals generally recover in two to five days without treatment.


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